Small hydraulic unit



Oct. 17, 1950 M, A, MATHYs 2,526,034

SMALL HYDRAULIC UNIT Filed June 2'7, 1947 4 Sheets-Sheet 1 FTQ@ .SECONDFEED FORWARD l l n J IN V EN TOR.

cman CH.. QHolthgs BY 6MM, m; Wwf ad# (fl-r-rorzNEY Oct. 17, 1950 M. A,MA1-HYS 2,526,034

SMALL HYDRAULIC UNIT Filed June 27, 1947 4 Sheets-Sheet 2 |o\ ooINVENTOR. Umax CH. Q'Y'locthgs 9o dl. /pm ,Mw/Mz x4 (f1-womens Oct. 17,1950 M. A. MATHYs 2,526,034

SMALL HYDRAULIC UNIT Filed June 27, 1947 4 Sheets-Sheet 5 FQ@ 5 RAPloTRAvERsE FoRwARo Fuga? RAPID TRM/Ease; QETURN INVENTOR.

th @/Ylolx ci, 67nd gs mi /Jm/ a (fl'rromvafs Oct. 17, 1950 M. A. MATHYs2,526,034

SMALL HYDRAULIC UNIT Filed June 27, 1947 4 Sheets-Sheet 4 FTQ@ STOPPosh-10N IN V EN TOR.

Patented Oct. 17, 1950 SMALL HYDRAULIC UNIT Max A. Ma'thys, Detroit,Mich., assigner to Ex-Cell-O Corporation, Detroit, Mich., a corporationof Michigan Application June 27, 1947, Serial No. 757,562

21 claims. 1

The present invention pertains generally to an improvement in ahydraulic power system of the general type disclosed in applicants priorPatent No. 2,416,339 and his copending application Serial No. 473,490,filed January 25, 1943, now Patent No. 2,427,970 issued Sept. 23, 1947.More specically, the invention relates to improved actuating means for ahydraulic control valve, having particular, but by no means exclusive,utility in a small, self-contained, hydraulic power unit for a machinetool.

One of the objects of the invention is to provide a unit of thecharacter set forth and having improved actuating means for the maincontrol valve whereby the necessity for pilotvalves, auxiliary actuatingvalves and complex mechanical linkages is completely eliminated.

Another object of the invention is to provide a valve member shiftableinto a plurality of control positions as an incident to the shifting ofan abutment member into a lesser number of positions. A related objectis to provide actuating means for the valve member comprising a movableabutment eifective to directly position the valve member in certainsteps of a sequence and to indirectly position the valve member in theremainder of the steps of such sequence.

A further object is to provide valve actuating means of the above typeincluding a plurality of means for applying forces to the valve memberand also including a means for governing the sequential application ofvarious force combinations to the valve member by the force-applyingmeans.

Still anotherobject is to provide a unit of the character set forth andhaving valve actuating means responsive to the actuation of apressuresensitive switch for automatically returning the valve to a stopposition when the pressure in the system exceeds a predetermined value.

A further object is to provide a hydraulic unit of the foregoing typeand which will be compact, simple, and suitable for high spindle speeds.

Other objects and advantages will become apparent as the followingdescription proceeds, and from the accompanying drawings, in which:

Figure 1 is a diagrammatic view of an exemplary system embodying thepresent invention.

Fig. 2 is a fragmentary side elevational view of the upper portion of anillustrative unit employing the system of Fig. 1.

Fig. 3 is a fragmentary plan view of the unit showninFig. 2.

Fig. 4 is a fragmentary transverse sectional view of the upper portionof the unit taken in the plane of line 4 4 in Fig. 2.

Figs. 5 through 8 inclusive are fragmentary vertical sectional viewstaken longitudinally through the main control valve with the latterrespectively shown in the Rapid Traverse Forward, First Feed Forward,Rapid 'Iraverse Return, and Stop positions.

Fig. 9 is an enlarged fragmentary vertical sectional view through thepump pressure limiting valve. l

Fig. 10 is a wiring diagram showing the various electrical controls forthe unit.

Figs. l1 and 12 are fragmentary views of a modied linkage for couplingthe movable core of the solenoid to the valve plunger.

While the invention is susceptible of various modifications andalternative constructions, a preferred embodiment has been shown in thedrawings and will be herein described in some detail, but it is to beunderstood that there is no intention to limit the invention to thespecific form disclosed, the intention being, on. the contrary, to coverall modifications.and'alternative constructions falling within thespiritand' scope of the invention as expressed in the appended claims.

Turning now to Fig. 1, an illustrative system embodying the presentinvention is there shown comprising a hollow housing which may bereadily bolted to any appropriate support (not shown). Mounted withinthe housing 20 are the various sub-assemblies that make up the completeunit, such as a variable delivery motor driven pump 2|, a hydraulicactuator 22, a, main control valve member 24, feed control orifices and26, and a pressure limiting valve 28.

The pump 2i is of the variable delivery class and preferably of theswash plate type, although other variable delivery pumps may be foundsatisfactory. Briefly, the pump includes a plurality of plunger devicescarried by a rotatable cylinder body 29, the plungers being arranged inan annular pattern with theiraxes parallel to the rotational axis of thecylinder body. A rcckable swash plate is pivotally mounted with its facein abutment with the outer ends of the pump plungers, the pivot pointbeing located so as to balance the plunger reaction on both sidesthereof. When the swash plate 30 is parallel the fluid delivery rate ofthe pump approaches its maximum value. The swash plate 30 is carried bya supporting block 3| having an adjusting arm 32 for altering ltheangular position of the plate. A tensile spring 34, which is connectedbetween a fixed point in the housing and the outward end of the arm 32,tends to urge the swash plate toward a position of maximum angularityand hence maximum fluid delivery. Also connected to the outward end ofthe arm 3 2 by means of a link 35 is a hydraulic plunger 36, the latterserving, when subjected to suillcient hydraulic pressure, to oppose thespring 34 and to rock the swash plate 30 into a parallel position withrespect to the end of the cylinder body 29, thus reducing the fluiddelivery rate of the pump.

The hydraulic actuator 22 comprises a tubular quill 38 which is mountedfor reciprocation in a cylindrical bore 39, the annular space betweenthese members serving as a piston chamber 40. The quill 38 rotatablysupports a tool spindle 4|, the details of which are not important here,

other than the fact that the spindle is supported for reciprocation aswell as rotation. Intermediate the ends of the quill, a sleeve-likepiston 42 is formed unitary therewith, and in the present instance thepiston is of the diiercntial type with its rearward area approximatelyequal to twice its forward area.

The main control valve 24 is provided for the purpose of governing themovements of the actuator 22. This is accomplished by interposing thevalve between the pump 2| and the actuator 22 and connecting thesemembers by means of suitable hydraulic conduits. Thus fluid is drawnfrom a reservoir or sump 44 via a suction line 45, is delivered by thepump 2| to the main control valve 24 via a pressure conduit 46 andbranch lines 48, 49, thence passing to one or both ends of the pistonchamber 40 via lines 59, 5|. Fluid may be exhausted from either end ofthe piston chamber 40 via the line 50 or 5|, leaving the main controlvalve 24 via branch line 52, 54, or 55 and entering an exhaust conduit56 which discharges into the sump 44. The adjustable feed orices 25 and26 are connected respectively into branches 54 and 55, the formerserving to meter into the exhaust conduit huid discharged from thecontrol valve 24. thereby varying the back pressure in a pump controlline 58 and thus regulating the rate of delivery of the pump`2|.

The main control valve 24 is of the reciprocable l as distinguished fromthe rotary type, being slidably disposed and axially shiftable within aported cylindrical bore 59 in the housing 20 and adapted to define anoperating cycle for the actuator 22. Basically, the valve comprises anaxially shiftable plunger or spool 6l) having a plurality of annularshoulders and grooves theref on which, in cooperation with the ports inthe cylindrical bore, permit the valve to be employed in a series ofsuccessive steps or control positions, including Stop, Rapid TraverseForward, First Feed Forward, Second Feed Forward, and Rapid TraverseReturn.. 'I'hese will be discussed below in the foregoing order.

in order to maintain the swash plate 30 substantially parallel to theend of the cylinder block 29 and thus keep the pump 2| in a condition ofminimum iiuid delivery. This arrangement is achieved by means of aninlet port 6| in the valve cylinder 59 connecting the branch line 49 tothe latter, an outlet port 62 in the valve cylinder connecting thelatter with the branch discharge line which in turn communicates withthe pump control line 58, and an annular groove 64 in the valve spool60, the groove partially overlying both of the ports 6|, 62. The circuitmay readily be traced by reference to Fig. 8, taken in connection withthe system illustrated in Fig. 1. Its course is as follows: pressureconduit 46, branch line 49, inlet port 6|, groove 64 of the valve spool,outlet port 62, branch discharge line 55, and pump control line 58. As anatural consequence of this position of the valve spool 66, somepressure fluid will pass from the groove 9i through a port 65 and thenceto the forward end of the actuator piston chamber @D via the conduit 5|.Because of the circuit just described` any pressure in such fluid willmerely produce a gentle restraining force upon the forward face of thepiston -42 tending to hold the actuator 22 in the retracted position.

Upon the initiation of the operating cycle, the spool of the valve 24 isshifted to its extreme right-hand or Rapid Traverse Forward position, asrepresented in Fig. 5, and which causes the actuator 22 to move in aforward or outward direction. When the valve is in this position, fluidunder pressure is conducted to both ends of the actuator piston chamber48 via the lines 50 and 5|, subjecting both sides of the piston 42Referring to Fig. 8, the main Lcontrol valve 24 i is shown in the Stopposition, from which it may be shifted rightwardly to begin an operatingcycle for the actuator 22. When the Valve 24 is in this position, theactuator is in its fully retracted position within the cylinder 39. Thepressure conduit 46, via its branch 49 is then directly connected to thepump control line 58 to pressure. Due to the diierence in area betweenthe forward and rearward sides of the piston 42, the latter will moveforward at a rate proportional to such area difference and alsoproportional to the pump discharge pressure.

Communication between the pressure conduit 46 v and the valve cylinder59 now occurs via the branch line 48 and an inlet port 66, as well asthrough the branch 49 and its inletv port 6|. Within the cylinder 59, anannular groove 68 in the valve spool connects the inlet port 6| with theport 65, While another annular groove' 69 in the spool 60 connects theport 66 with a port 10. These grooves permit fluid under pressure toenter the actuator lines 59 and 5| through the ports 19 and 65, passingfrom the former to their respective ends of the piston chamber 49.Although pressure is applied to both sides of the piston 42, it will benoted that there is no return flow of fluid from the actuator 22 to theexhaust line 56, the lands ofthe valve spool 60 completely isolating thedischarge lines 52, 54, 55 from the actuator lines 56, 5|. Due also tosuch isolation, the pump control line 58 is allowed to communicate withthe exhaust conduit 56 and the pump 2| therefore operates at maximumiiuid delivery.

Turning to Fig. 6, the First Feed Forward position of the valve 24 isthere shown, the valve spool 60 having been shifted one step to theleft. Under this condition, the valve is arranged to admit fluid underpressure to the rearward end of the piston chamber 40 and exhaust itfrom the forward end at a predetermined rate governed by the setting ofthe rst feed orifice 25. The application of pressure to the largerearward area of the piston 42 produces the substantial force necessaryto move the actuator 22 and the tool spindle 4| against the resistanceoffered by the workpiece, while the use of the orice 25 in the exhaustcircuit from the piston chamber 40 insures that the actuator will beadvanced at the proper feed rate. For the purpose of obtaining a pumpdelivery rate commensurate with the feed rate determined by the settingof the first feed orifice, the valve 24 connects the discharge line fromthe piston chamber 40 to the pump control line 58. The foregoingcircuits may be followed by reference to Figs. 1 and 6. Fluid underpressure passes from the branch 48 of the pressure conduit 46 and intothe valve cylinder 58 via the inlet port 66. The annular groove 69 inthe valve spool 68 connects the port 66 with the-port 18 andthe actuatorconduit 50, the latter admitting the pressure fluid to the rearward endof the piston chamber 40. Fluid discharged from the forward end of thechamber 48 is conducted by the actuator line 5| to the port 65, fromwhich it passes along the annular groove 64 in the valve spool. Thegroove 64 is positioned to overlie the exhaust port 62 of the exhaustbranch line 55, and to overlie partially a port 1I communicating withthe exhaust branch line 54. The latter conducts the discharged uid tothe first feed orifice 25 which meters it into the exhaust conduit 56.Fluid entering the port 62 is directed by the branch line 55 into thepump control line 58 for the purpose already explained. The second feedorifice 26, being by-passed in this arrangement, is thereby renderedineffective.

The valve 24 in its Second Feed Forward position is illustrated in Fig.1, the spool 68 having been moved another step to the left. The valve 24now admits fluid under pressure to the rearward end of the pistonchamber 40 and permits it to be exhausted therefrom at a predeterminedrate governed by the settings of both the feed orifices 25 and 26.Pressure fluid is applied to the rearward area of the piston 42 in thesame manner as that obtaining in the First Feed Forward position,namely, from the pressure conduit 46 into the cylinder 59 via the branchline 48 and the inlet port 66, along the annular groove 69 in the valvespool 68, out through the port 18 and into the rearward end of thepiston chamber 40 via the actuator line 50. Fluid discharged from theforward end of the chamber 40 passes into the cylinder 59 via theactuator line 5I and the port 65. However, the groove 64 now overliesonly the ports 65 and 62, the port 1| of the branch line 54 beingisolated from the port 62 by an annular land 12 on the valve spool. Thusthe discharged fluid is conducted from the port 65 to the port 62, viathe groove 64, thence passing along the branch line 55 through thesecond feed oriflce 26 and also through the first feed oriilce 25,finally entering the exhaust conduit 56 which empties into the sump 44.Since the orifices are connected in series under the above conditions,the piston 42 and consequently the actuator 22 will move outwardly at arate determined principally by the sum of the restrictive effects of theorifices. In the event that the latter when in series provide moreresistance to fluid flow than is needed to achieve a given rate ofactuator movement, such rate may be increased through the expedient ofby-passing a relatively small quantity of the fluid discharged from theorifice 26, via the branch line 54, the port 1l, an annular groove 14 inthe valve spool which barely communicates with the port 1I, an exhaustport 15, and the branch 52, to the exhaust conduit 58. As in the case ofthe First Feed Forward position, fluid from the branch line 55 isadmitted to the pump control line 58 for the purpose of securing theproper fluid delivery rate.

The Rapid Traverse Return position of the valve 24, and which representsthe extreme leftward position of the valve spool 60, is shown in Fig.'1. The main branch 48 of the pressure conduit 46 is now completelyblocked off by a land 16 on the valve spool, and consequently no fluidunder pressure is supplied to the rearward end. of the piston chamber 40or the rearward face of the piston 42. Pressure fluid is, however,admitted to the forward end of the chamber 40, exerting a force on thepiston 42 tending to return the actuator to its retracted position. Thiscircuit includes the branch 49, the intake port 6 I, the annular groove64, the port 65, and the actuator line 5I which communicates with thechamber 40. Fluid discharged from the rearward end of the chamber 40passes through the actuator line 50, and port 10, the annular groove 69,the exhaust port 15, and thence to the branch 52 of the exhaust line 56.The application of fluid pressure to the forward face of the piston 42,together with the unrestricted exhaust path for the fluid dischargedfrom the rearward end ofthe piston chamber 40, results in a high speedreturn of the actuator 22 to its retracted position, thus completing theoperating cycle. Another contributing factor to such speed is the factthat the pump control line 58 is connected directly to the exhaust line56 via the ports 62, 15, and the groove 14 in the valve spool, producingthe maximum fluid delivery rate for the pump.

Actuation of control valve For the purpose of moving the plunger of thevalve 24 through a series of successive steps in timed relation to theaxial movements of thc actuator 22 and the tool spindle 4|, therebydening an operating cycle, means are provided for the application offour external forces to the plunger 68." These forces are appliedsequentially in combinations governed by the position of still anothermeans in the form of a movable abutment member, which, althoughshiftable into a lesser number of releasable positions than the valveplunger, actually causes the plunger to occupy a greater number ofpositions than such means. In the illustrative embodiment (Fig. 1 to 8inclusive), the movable abutment comprises a rocker arm 18 dependingfrom a pivotal support 19 carried by an extension 80 of the unit housing20. An adjustable frictional device such as a disk spring 8l isassociated with the support 80 for enabling the arm to withstand apredetermined force without moving.

The rocker arm 18 is coupled to two other members of the valve assembly,namely, the valve plunger 60 and a limit switch LS, by means of a pairof lost-motion connections. For engaging the valve plunger, the arm 18is provided with a rigidly attached transverse pin 82 disposed betweenand projecting into the pathv of a pair of axially spaced apartshoulders 84, 85, formed in the valve plunger adjacent its rearward orinner end. For engaging the limit switch LS, the arm 18 has associatedtherewith an operating bar 86 having abutments interposed in the path ofthe lever near each extreme of its travel. Preferably, the bar 86 isformed as a flat plate with an elongated slot for the lever, asindicated in Fig. 2, but for purposes of clearer illustration the barhas been represented in Figs. 1 and 5 to 8 as a rod carrying abutmentsin.the form of a pair of spaced apart nuts 88, 89 which are e'igageablewith the arm '|8.

The force-applying means earlier referred to include a longitudinallymovable dog bar or tripping bar 90 rigidly coupled at its outer end tothe bearing housing of the tool spindle 4|, as indicated schematicallyin Fig. 1, and arranged to move the rocker arm 'I8 through a series ofsuccessive angular positions with respect to the axis of the valveplunger 60; electromagnetic means such as a solenoid 9| having a movablecore 92 and acting through a slidable tension rod 94 and an internalcompression spring 95 which are housed within an axial bore 96 in thevalve spool 60, as shown in Figs. 1, and 5 to 8; the disk springfriction means 8| associated with the pivotal mounting of the arm 18,illustrated in Fig. 4; and a relatively weak second compression spring98 encircling the forward or outer end of the valve spool 60, beingdisposed between an adjustable collar 99 threaded on the valve spool andthe unit housing 20 so as to exert a yieldable thrust or bias tending tomove the spool 60 to the extreme left.

Referring more particularly to the drawings just mentioned, the dog bar90 has a T-shaped slot |00 milled therein for receiving a plurality ofaxially adjustable, spaced-apart tripping dogs. In the embodimentillustrated, going from left to right, these include a stop dog |0|, aone-directional flrst feed dog |02, a one-directional second feed dog|04, and a reverse dog |05. The end of the rocker arm 18 is slightlynarrower than the width of the upper portion of the slot |00, enablingit to be projected into the slot and consequently into the path ofmovement of the dogs. Thus each dog is arranged to apply a positive,intermittent force to the valve spool 60 at a different point in thecycle, assuming the slack has been taken up in the lost-motionconnection between the rocker arm and the valve spool.

As already indicated to some extent, one of the means for taking up theslack in the lost-motion connection between the arm 18 and the valvespool 60 comprises the solenoid 9|. When the latter is energized, ayieldable thrust is exerted upon the valve spool 60 through the movablecore 92 of the solenoid, the tension rod 94, and the internalcompression spring 95, tending to move the valve spool to the right.This thrust or force is transmitted to the rocker arm through theshoulder 84 and the transverse pin 82.

After a dog has passed out of contact with the lower end of the rockerarm 18, the friction means 8| associated with the pivot thereof becomeseffective to hold the arm in the position determined by such dog untilthe arm is acted upon by the next dog, the means 8| offering a force inopposition to any thrust produced by the solenoid 0| as well as to thebiasing force of the external compression spring 98.

The small biasing force of the external compression spring 98 isconstantly exerted upon the forward or outer end of the valve spool 80,tending to urge the former to the extreme left or Rapid Traverse Returnposition shown in Fig. '7. 'I'his force is rendered effective only afterthe solenoid 9| has been deenergized and the rocker arm has been movedclockwise from the position it occupies when the valve spool is in theStop position.

The relationship of the various positioning means discussed above willbe better understood following a brief description of the manner inwhich they are coordinated to actuate the valve 8 24. Considering rstthe Stop position, illustrated in Fig. 8, it will be observed tnat therocker arm '|8 occupies its extreme counterclockwise position, havingbeen moved there by the stop dog |0| on the dog bar 90. The solenoid 9|,being deenergized, exerts no force on the valve spool 60 and, as aconsequence, the latter is shifted leftwardly by the externalcompression spring 98 so as to bring the shoulder 85 into abutment withthe pin 82 of the rocker arm 18. With the spool 60 in the positionshown, the fluid delivery rate from the pump 2| is held at a minimum andthe actuator 22 remains in its fully retracted condition. Assume nowthat the solenoid 9| becomes energized by the depression of anappropriately connected starting switch. The valve spool 60 will beimmediately shifted to the right due to the thrust exerted thereonthrough the movable core 92, the tension rod 94, and the internalcompression spring 95, bringing the shoulder 84 into abutment with thepin 82 of the rocker arm '18, and thereby taking up in one direction theslack in the lost-motion connection between the rocker arm and the valveplunger or spool. Notwithstanding the fact that such slack or lostmotionis fully taken up by the thrust of the solenoid, the friction means 8|serves to prevent the rocker arm from being rotated in either directionexcept in response to the considerable force exerted by the dog barthrough the tripping dogs. The valve spool 60 is now in the RapidTraverse Forward position, shown in Fig. 5, causing the actuator 22 tomove leftwardly or forwardly and to pull with it the dog bar 90. Thiscontinues until the rst feed dog |02 is cammed against the lower end ofthe rocker arm 18, rotating the latter clockwise through a predeterminedangle. Since the solenoid remains energized, the pin 82 will remain inabutment with the shoulder 84 and the valve spool 60 will therefore bepositively positioned in response to the positioning of the rocker arm,which further compresses the spring 95. The valve spool 60 is now in theFirst Feed Forward position, as indicated in Fig. 6, and the actuator 22will continue its leftward or forward movement at a feed ratepredetermined by the setting of the first feed orifice 25. This motioncontinues until the second feed dog |04, which projects higher than thedog |02, engages the lower end of the rocker arm 18, shifting the latterclockwise through another angle. The abutting relationship between theshoulder 84 and the pin 82 persists due to the fact that the solenoid 9|is still energized, enabling the rocker arm 18 to move the valve spoolpositively and directly into the Second Feed Forward position,illustrated in Fig. l. The leftward or forward motion of the actuator 22will continue but at a feed rate determined principally by the combinedsettings of both feed orifices 25 and 28. The dog bar 90 of course moveswith the actuator 22, eventually bringing the reverse dog |05 to a pointwhere it cams the rocker arm 18 clockwise to the extreme position of thelatter. As an incident to its clockwise travel, the arm |8 is broughtinto engagement with the left abutment 88 of the limit switch operatingbar 88, moving the latter to the left and opening the limit switch LS.Due to the fact that the switch LS is connected in series with thesolenoid 9|, the opening of the former will deenergize the solenoid andthereby permit the valve spool 60 to be moved to its extreme leftposition under the biasing force of the external compression spring 9B,at the same time tilt out of the way in the event of contact with I thelower end of the rocker arm 18. The latter, however, remains in itsextreme clockwise position until engaged bythe stop dog where- `upon itis moved counterclockwise to the position indicated in Fig. 8. As anincident to the coun- "terclockwise motion of the rocker arm, the pin 62moves across the lost-motion space and into abutment with the shoulder85, rendering the rocker arm effective to move the valve spool 60positively and directly to the right until it occupies the Stop positionshown in Fig. 8. The rocker arm in the course of its counterclockwisemovement also closes the limit switch LS due to engagement with theright-hand abutment 89 of the switch operating bar 86. Depending uponthe arrangement of the electrical controls, the closing of the limitswitch may or may not be eiective to energize the solenoid 9| andinitiate another operating cycle.

It will be appreciated from the foregoing that the rocker arm 18, byreason of being shifted through a series of four successive angularpositions, is utilized to dene accurately the ve sucl'cessive steps orcontrol positions assigned to the valve spool or plunger 60. Due to theuse of the lost-motion connections between the rocker arm, the valveplunger, and the limit switch, the rocker arm is rendered effective whenthe solenoid is energized to directly position the valve plunger incertain of the successive steps or control positions of the latter, thearm also being rendered effective when the solenoid is deenergized t0indirectly position the plunger in the remainder of the controlpositions thereof. Thus the plunger 60 is directly positioned by therocker arm 18 in the steps of Stop, Rapid Traverse Forward, First FeedForward, and Second Feed Forward; the plunger is indirectly positionedby the rocker arm in the step of Rapid Traverse Return.

Electrical control circuit Turning to the schematic wiring diagram ofFig. it will be noted that three phase A. C. power is supplied to theunit through the lines LI, L2, L3 and main line switch |06. Anelectrical motor |08, which serves as the driving means for the entireunit, obtains power from this supply through contacts CRI-2, 3 and 4 ofa motor control contactor CR-I. Power for a single phase control circuitLIO, L30 is derived from phase LI, L3 through a control transformer |09.This circuit includes the motor control contactor CR-I, the solenoid 9|,and a contactor CR2 for the solenoid, together with various controlswitches. The motor |08 is controlled by means of the contactor CR-Iwhich, when energized in response to the closing of a started switchI|0, completes a circuit through the line contacts CRI-2, 3 and 4, v

also simultaneously closing a pair of sealing-in contacts CRI-I, thelatter being connected in parallel with the starter switch. The motor isstopped by depressing the plunger of a stop switch III which interruptsthe circuit of the contactor CR-I, thereby opening the contacts l0 CRI-Iand CRI-2, 3 and 4. The contacter CR2 is arranged to energize thesolenoid 9| through the closure of contacts CR2-l. To this end, there isconnected in series with the contactor the limit switch LS, a cyclestarter switch II2, a. selector switch |I4, and an emergency cycle stopswitch I I5. A pair of sealing-in contacts CR22 are connected inparallel with the switches I I2 and 4 for holding in the contactorfollowing the momentary closure of the switch l I2. Assuming that theplunger 60 of the valve 24 is in the Stop position and that the limitswitch LS is therefore closed, if it be desired to initiate only asingle complete operating cycle the selector switch I I4 would be raisedto its upper position. The emergency cycle stop switch I|5 beingnormally closed, it then becomes possible to energize the contactor CR2and hence the solenoid 9| by momentarily depressing the plunger of thecycle starter switch I I2, the sealing-in contacts CR2-2 servingthereafter to keep the circuit closed. The energizing of the solenoid 9|serves to shift the valve spool 60 into the Rapid Traverse Forwardposition and the actuator 22 is consequently put through the previouslydescribed steps of the operating cycle. When the actuator reaches theforward extreme of its travel, the reverse dog |05 engages the rockerarm 18 causing the latter to open the limit switch LS, deenergizing thecontactor CR2 and consequently the solenoid 9|. 'I'he actuator 22 isthereupon returned automatically to the Stop po. sition, therebycompleting the cycle. Note that the closing of the limit switch upon thereturn of actuator to the Stop position is ineffective to initiateanother cycle with the arrangement just described. If it be desired thatthe cycle should be automatically repeated, it is merely necessary tomove the selector switch I I4 to its lower position (indicated in brokenlines in Fig. 10), th'us rendering the limit switch effective toinitiate the next cycle automatically upon the completion of thepreceding one.

Safeguards Various safeguards, both hydraulic and electrical, areincorporated into the unit to make it more reliable and foolproof thanprior units. Referring to Figs. 1 and 9, one hydraulic safeguard residesin the use of the overload valve 28. This valve comprises a stationarybushing I I8 mounted within a suitable bore I I9 in the unit housing.Formed at either end 0f the bore and in communication therewith are anupper pressure chamber |20 and a lower pressure chamber I2I. A hollowplunger |22 is slidably disposed within an axial bore |23 in the bushingI|3 and is held in place by means of a compression spring |24 actingupon its upper end through a collar |25. Radial passages |26 and |28 inthe plunger respectively connect a .small diameter axial bore |29, whichis closed at both ends, with annular peripheral grooves |30 and |3| thegroove |30 being tapered and located in the upper portion of theplunger. Intermediate its ends, the bushing IIs is also provided with apair of annular grooves I 32, |34 in its external periphery and whichcommunicate with the bore |23 therein via radial passages |36 and |38,respectively. The lowermost pressure chamber I2I of the valve isconnected to the pressure conduit 46 via a branch line |39 while theupper pressure chamber |20 communicates with the pump control line 58via a branch line I 40. The uppermost annular grove |32 in the bushingIIB is connected directly to the exhaust conduit 56 through the branchI4I. In operation, the plunger |22 occu- 11 pies the position shown inthe drawings as long as the pressure in the conduit 46 remains below apredetermined value, and there is no vflow of fluid through therestricted bore |29 since the lower peripheral groove |3| is completelyblocked oii. If the pressure in the conduit 46 exceeds the predeterminedmaximum value, the plunger |22 is forced upwardly, bringing its lowerannular groove |3| into registry with the passage |38 in the bushing andconnecting its upper annular groove |30 with the upper pressure chamber|20. Thus high pressure fluid is conducted from the chamber |2|, throughthe passages of the plunger |22 and into the upper chamber |20, fiowingtherefrom to the branch line |40 and finally to the pressure controlline 58. The suddenly increased pressure in the line 58 immediatelycauses the Vswash plate 30 of the pump to assume its parallel position,minimizing the fluid delivery rate of the pump.

Another hydraulic safeguard resides in the fact that in the event of afailure of electrical power, the constant biasing force of the externalcompression spring 98 will immediately become effective to shift thevalve spool 50 to either the Rapid Traverse Return or the Stop position,depending upon the angular position of the rocker arm at the time of thefailure.

One of the electrical safeguards already mentioned is the emergencycycle stop switch ||5. The opening of this switch deenergizes both thecontactor CR-Z and the solenoid 9|, and the switch is susceptible ofactuation at any point in the operating cycle of the unit. Once havingbeen opened, the switch does not automatically return to a closedposition, but must be deliberately closed through the use of a manualreset |42. Ordinarily, manual means alone will be found satisfactory foractuating the switch H5. However,. if desired a pressure controlledactuator |44, shown schematically as a bellows, may be mounted adjacentthe operating arm of the switch |5 for opening the latter in the eventtha-t the pressure in the system becomes excessive. Such a conditionmight arise, for example, upon the breaking of a tool in the spindle 4|during one of the feeds of the cycle. Should something of this natureoccur, the opening of the switch ||5 immediately deenergizes thesolenoid 9|, permittingr the valve plunger '60 to be shifted immediatelythrough Stop and into the Rapid Traverse Return position. In lieu of thearrangement described, an equally good alternative would be the use of aseparate pressureactuated switch in series with the switch |5 but havingits own manual reset.

The use of a pressure controlled device with the switch I5. or the useof a separate pressureactuated switch in series therewith, and may beselectively employed to provide a dwell control feature in the unit.This is helpful where it is necessary to hold the actuator 22 at itsforward extreme of travel long enough to complete a facing-off orsimilar operation. In such event, a rigid mechanical abutment is placednear the forward end of the path of the actuator 22, and whenencountered by the latter a large increase in pressure results. Byinterposing a time delay device between the pressure actuator and theswitch it becomes possible todelay the automatic return of the valveplunger and hence the actuator for the desired period of dwell. If suchan arrangement is utilized, the closing of any manual reset which mightbe used is made ineffective to initiate another cycle until the closingof the cycle starting switch ||2. When operating on a cycle includingdwell return, the pressure-actuated switch does not serve as an overloadprotective device, and consequently it becomes necessary for-theoperator to observe the action of the tool to avoid jamming due tobreakage or other causes.

Synopsis of operation While various phases of operation have beenseparately discussed above, it will be helpful to present at this stagean overall picture of the manner in which the unit Works. Assume firstthat the actuator 22 is in the fully retracted position and that theplunger of the control valve 24 is occupying the Stop position asindicated in Fig. 8.v Under the conditions illustrated, the branch 48 ofthe pressure conduit 46 is completely blocked oi and the fluid from thebranch 49 is short circuited into the pump control line 58 via the inletport 6|, the groove 64, the port 52 and the branch line 55. This forcesthe pump control plunger 38 downwardly and causes the swash plate 30 toassume the minimum fluid discharge position. The operating cycle is theninitiated by the momentary depression of the plunger of the cyclestarter switch ||2, energizing the contactor CR-2, which, in turn, energizes the solenoid 9| through the closure of the The movable core 92 ofthe solenoid, together with the tension rod 94 is thereby drawn to theright, exerting an axial thrust in that direction upon the valve spoolor plunger 60 through the internal compression spring 95. Consequently,the spool 60 is moved to the right until its shoulder 84 is brought intoabutment with the pin 82 of the rocker arm 18. The frictional meansadjacent the pivot of the rocker arm enables the latter to withstand thethrust of the solenoid, thereby accurately locating the valve spool inthe Rapid Traverse Forward position, shown in Fig. 5.

With the valve in the Rapid Traverse Forward position, pressure iluid isapplied to both ends of the piston chamber 40, causing the piston 42 ofthe actuator 22 to advance forwardly or outwardly at a rate proportionalto the ratio between the areas of the rearward and forward faces of thepiston. Briefly, the rearward pressure circuit includes the branch 48,the inlet port 66, the groove 69, the port 10, and the actuator line 50;the forward pressure circuit comprises the branch 49, the inlet port 6|,the groove 68, the port 65, and the actuator line 5|. Maximum fluiddelivery from the pump is obtained by connecting the pump control line58 to the exhaust conduit 56 via a circuit including the branch 55, theport 52, the groove 64, the port 15, and the exhaust branch 52. With theadvance of the actuator 22, the dog bar is also drawn leftwardly,bringing the first feed dog |02 into engagement with the rocker arm 18and rotating the latter clockwise through a small angle until itoccupies the position shown in Fig. 6. Since the solenoid 9| is stillenergized, the shoulder 84 remains in abutment with the pin 82, and therocker arm in its new position therefore defines a new position for thevalve spool 60. This is the First Feed Forward position, wherebypressure fluid is applied to the rearward face of the piston 42 via thebranch 48, the inlet port 68, the groove 69, the port 10, and theactuator line 50. Fluid discharged from the forward end of the pistonchamber -40 is metered through the first feed oriflce 25, causing theactuator to advance the tool 13 lspindle at a feed rate predetermined bythe setting of that lorice. The course of this discharged uid includesthe actuator line the port 65, the groove 64, the port 1|, and thebranch line 54. Since the groove 64 overlles both ports 62 and 1|, someof the fluid is admitted to the` pump control line to maintain a iluiddelivery rate also determined by the setting of the orifice 25. Underthese conditions the actuator 22 and the dog bar 90 will continue toadvance, bringing the second feed dog |04 into engagement with therocker arm 18 and rocking the latter clockwise through another angle tothe position indicated in Fig. 1. Since the solenoid 9| remainsenergized, it ycontinues to take up the lost motion in the connectionbetween the rocker arm 'I8 and the valve spool,60, thereby enabling thearm to position the valve spool once more, this time in the Second SpeedForward position. The hydraulicconditions obtaining under thesecircumstances are rather similar to those existing for First FeedForward, exceptfor the fact that the combined restrictive elfect of theorifices in series is now lutilized to govern the rate of feed. Thuspressure is applied to the rearward end of the piston 42 via the branch48, the inlet port 66, the groove 69, the port l0, and the actuator line59. Fluid is discharged from the forward end of the land 12 from theport 62, although a smallV portion of the fluid discharged from theorifice 2S' might be diverted directly into the exhaust line through thebranch 54, the portll, the groove 14, the port 15, and the exhaustbranch 52. Because of the direct connection between the pump controlline 58 and the branch 55, the back pressure in the latter, which isdetermined by the orifice settings, will govern the fluid delivery rateof the pump. The actuator and the dog bar 99 will continue to move tothe left at the second feed rate until the reverse dog |05 engages therocker arm 18. The arm is thereby moved to its extreme clockwiseposition, and as an incident to such motion it opens the limit switchLS, deenergizing the solenoid 9|. This releases the thrust on theinternal compression spring 95. permitting the external compressionspring 98 to take charge, the latter moving the valve spool 60 to itsextreme leftward or Rapid Traverse Return position. Note, however, thatthe shoulder 84 now no longer abuts thepin 82 of the rocker arm. Thevalve in this position admits pressure fluid to the forward end of thepiston vchamber 40 via they branch conduit 49, the inlet port 6|, thegroove 64, the port 65, and the actuator line 5| Fluid is dischargedfrom the rearward end of the piston chamber via the actuator line 50,the port 19, the groove 69, the exhaust port 15, and the branch 52 ofthe exhaust conduit 56. The pump control line 58 is also directlyconnected to the exhaust line via the branch 55, the port 62, the groove14, the exhaust port 15, and the branch 52, causing the pump to beoperated at the maximum uid delivery rate and therefore producing arapid retraction of the actuator. This rearward travel of the actuatorcontinues until the stop dog |0| engages the'rocker arm 18,

moving it together with the valve spool 69 to the Stop position andclosing the limit switch LS. If the selector switch I4 is in its upperor solid line position, as shown in Fig. 10,' thecycle will not repeatautomatically. If, however, the switch 14 ||4 happens to be in its loweror broken line position, the closing of the limit switch LS willimmediately be effective to repeat the cycle automatically without firstclosing the cycle starting switch ||2.

M odz' ycation For the purpose of insuring still further the positivepositioning of the valve plunger 60 under the most adverse conditions, aslightly modified linkage for coupling the latter and the movable core92 of the solenoid 9| is provided. In a valve of the type described, theplunger may occasionally become sticky in its operation due, forexample, to continued idleness or to a phenomenon known in the art ashydraulic pressure lock. Stickiness due to the former condition is mostapt to occur at the start of an operating cycle when the valve plungeris in the Stop position. Stickiness due to the latter or pressure lockcondition may occur during a cycle when the valve plunger is in theSecond Feed Forward position immediately prior to moving to RapidTraverse Return.

In Figs. 11 and 12, an illustrative embodiment of the modified couplinglinkage is shown. Thus the valve plunger 6|) is formed adjacent its lefthand end with a relatively short axial bore |45 of somewhat greaterdiameter than the bore 96, the ends of the bores meeting to define anannular abutment or shoulder |46. In the region of its extremities, thetension rod 94 is provided with suitable abutting surfaces forrespectively engaging the shoulder |46 at one end of the plunger 60 andan external annular face |48 at the opposite end thereof. Accordingly,the left hand end of the rod 94 carries rigidly xed thereto a largewasher |49 of smaller diameter than the bore but of suicient size tohave substantial overlap with the shoulder |46. Unitary with the righthand end of the rod 94 is a head portion |50 adapted lfor pivotalattachment to the solenoid core 92 and having a pair of coplanarshoulders |5|, |52 adapted to abuttingly engage the face` |48 on theright hand end of the plunger 6|). In addition to the foregoing, theopen-ended collar 99 may be replaced by an adjustable cap |54 threadedon the plunger and blocking off the ends of the bore |45 to keep outforeign material.

In operation, assume that the valve plunger vis in the Stop position ofFig. 8. Upon the energizing of the solenoid 9|` at the start of a cycle,the movable core 92 shifts to the right, exerting through the tensionrod 94 and its washer |49 a force in excess of the pressure of thespring 95,

and capable of`fully compressing the same. During this time, if thevalve plunger does not -move in response to they reaction of the spring95 to the compression force thereon, the plunger 68 will receive ahammer blow upon the engagement of the washer |49 with the shoulder |46.As a result of such impact, the valve plunger 6U will be jarred free,whereupon it will be shifted into the Rapid Traverse Forward position bythe action of the spring 95. and the continued rightward movement of thesolenoid core 92.

Assume lfurther that the cycle has progressed to a point at which theplunger is in the Second Feed Forward position. As the reverse dog |05cams the rocker arm 18 into engagement with the abutment 88 of the limitswitch bar 96, the solenoid becomes deenergized. The spring whichheretofore had been under compression, is now released suddenly,accelerating the tension rod 94 and the movable core 92 to the left andproducing a sharp impact between the shoulders IBI, |52 of the tensionarm and the external face 148 of the valve plunger. The force of thisimpact tends to break the plunger 60 loose from the Second Feed Forwardposition, rendering the spring 98 effective to shift the former throughStop and into the Rapid Traverse Return position.

I claim as my invention:

1. A hydraulic control system for machine tools and the like comprising,in combination, an actuator, a variable delivery pump, a sump, pressureand exhaust conduits leading from the pump and the sun;4 `respectively,conduits leading from said actuatoa main control valve connected withsaid pressure and exhaust conduits and said conduits leading from saidactuator for delivering thereto fluid under pressure and receiving fluiddischarged therefrom, a reciprocable valve spool slidably disposedwithin a ported cylindrical .bore in said main control valve fordefining a stepped sequence of actuator movements including the steps ofrapid traverse forward, first feed forward, second feed forward, rapidtraverse return. and stop, a rocker arm movable into a number ofpositions less than the number of said steps and having a lost-motionconnection with said valve spool, electromagnetic means resilientlyconnected to said valve spool and arranged when energized to exert aforce tending to take up the slack in the lost-motion connection therebypermitting said rocker arm to positively position said valve spool,spring means also connected to said valve spool so as to exert anopposing but weaker force than that of said electromagnetic means, a dogbar rigidly attached to said actuator and having a plurality of trippingdogs for positively positioning said rocker arm, and switch meansoperable by said rocker arm to deenergize said electromagnetic means andthereby permit said spring means to position said valve spoolindependently of said rocker arm.

2. A hydraulic control system for machine tools and the like comprising,in combination, an actuator, a variable delivery pump, a sump, uidconduits leading from the actuator, the pump and the sump respectively,a main control valve interposed in said conduits for delivering fluidunder pressure to said actuator and receiving iluid dischargedtherefrom, a reciprocable valve spool slidably received within a portedcylindrical bore in said main control valve for defining by means of apredetermined series of axial positions a stepped sequence of actuatormovements including the steps of rapid traverse forward, rst feedforward, second feed forward, rapid traverse return, and stop, a pair ofaxially spaced-apart shoulders in said valve spool adjacent one endthereof, a rocker arm movable into a number of positions less than thenumber of said steps and having a lost-motion connection with saidshoulders of said valve spool, a solenoid having a movable coreresiliently connected to Asaid valve spool through a plunger and acompression spring housed within the latter, said solenoid arranged whenenergized to/'exert a force tending to take up the slack in thelost-motion connection causing said valve spool to move positively withsaid rocker arm, an external compression spring connected to said valvespool so as to exert an opposing but weaker force than that of saidsolenoid, a, dog bar rigidly attached to said actuator and having aplurality of spaced-apart tripping dogs for positively positioning saidrocker arm and also said valve spool when said solenoid is energized,and a limit switch operable by said rocker arm in one of its positionsto deenergize said solenoid and thereby permit said external compressionspring to position said valve spool independently of said rocker arm.

3. In a hydraulic power unit of the character set forth, the combinationcomprising a valve spool axially shiftable into a plurality ofpositions, and means including a rockable abutment member having alost-motion connection with said valve spool. means for shifting saidrockable abutment member into a lesser number of positions than saidvalve spool, and biasing means for taking wp the slack of saidlost-motion connection in either direction, thereby permitting saidrockable abutment member to define all the positions of said valvespool.

4. In a hydraulic power unit of the character set forth and including amain control valve having a ported bore, the combination comprising avalve spool slidably disposed within the bore and shiftable into aplurality of positions, a movable abutment member having a lost-motionconnection with said valve spool for shifting the same into saidplurality of positions as an incident to being shifted itself into alesser number of positions, and opposed but coacting biasing means fortaking up the slack of said lost-motion connection in either direction.

5. In a hydraulic power unit of the character set forth. the combinationcomprising a main control valve having a ported cylindrical bore, avalve spool slidably disposed within the bore and .axially shiftableinto a plurality of control positions, a rocker arm associated with saidvalve spool and having a lost-motion connection therewith, releasablemeans for taking up in one direction the slack in the lost-motionconnection between said rocker arm and said spool, and resilient meansarranged to act upon said spool in opposition to said releasable meansfor taking up the sack in the opposite direction, said latter meansbecoming effective to take up such slack upon the release of saidreleasable means in response to the position of said rocker arm.

6. In a hydraulic power unit of the character set forth, the combinationcomprising a. main control valve having a ported cylindrical bore, avalve spool slidably disposed within the bore and axially shiftable intoa plurality of control positions, spaced-apart abutments in said valvespool adjacent one end thereof, a rocker arm associated with said valvespool and having a lostmotion connection with the latter between saidabutments, releasable means including a solenoid for taking up in onedirection the slack in said lost-motion connection, and a compressionspring mounted for engagement with said spool and arranged to actthereupon in opposition to said releasable means for taking up the slackin the opposite direction, said compression spring becoming effective totake up such slack upon the release of said releasable means in responseto the position of said rocker arm.

'7. In a hydraulic power unit for a machine tool, the combinationcomprising an axially slidable valve plunger, a spring yieldably urgingsaid plunger toward one extremity of its path vof axial movement, meansincluding a movable abutment member having a lost-motion connection withsaid plunger for positioning the latter axially in either direction,means for shifting said abutment to a series of successive positionsaxially of said plunger and releasably holding the same in each of suchpositions, and means including a solenoid for compressing said spring 17and retaining said plunger against said abutment at the extreme of lostmotion opposite that toward which said spring tends to urge said valveplunger.

8. In a hydraulic power unit for a machine tool, the combinationcomprising a main control valve having an axially shiftable valveplungcr, axially spaced-apart shoulders in said valve plunger adjacentone end thereof, a rocker arm associated with said valve plunger andhaving an abutment projecting between said shoulders to produce alost-motion connection with the latter, a dog bar for moving said rockerarm through a series of successive angular positions with respect to theaxis of said valve plunger, a solenoid having a movable core connectedto said valve plunger by means ,of a rst compression spring housedtherein and adapted when energized to exert a resilent thrust upon saidlost-motion connection eliminating the slack in one direction, a secondL;

compression spring mounted for engagement with said valve plunger andarranged to act thereupon in opposition to the thrust of said solenoidfor taking up the slack in said lost-motion connection in the oppositedirection, and switch means operable as an incident to the :positioningof said rockerarm to deenergize said solenoid, said second compressionspring becoming effective to take up slack upon the deenergizing of saidsolenoid by the positioning of said rocker arm.

9. In a hydraulic power unit for a machine tool, the combinationcomprising a main control valve having an axially shiftable valveplunger, axially spaced-apart shoulders in said valve plunger adjacentone end thereof, a rocker arm associated with said valve plunger andhaving a transverse pin projecting between said shoulders to produce alost-motion connection with the latler, a movable bar having a pluralityof spacedapart tripping dogs arranged for moving said rocker arm througha series of successive angular positions with respect to the axis ofsaid valve plunger, friction means associated with said rocker arm formaintaining the latter in any given one of said series of successiveangular positions until moved into the next one of said series by anyone of said tripping dogs, a solenoid having a movable core connected tosaid valve plunger by means of a tension rod and a first compressionspring housedtherein, said solenoid being adapted when energized toexert a resilient thrust iny one direction upon said lost-motionconnection thereby bringing one of said shoulders into abutment withsaid transverse pin, a second compression spring mounted for engagementwith said valve plunger for exerting a yieldable thrust tending to urgethe opposite one of said shoulders into abutment with said transversepin, and switch means mounted adjacent said rocker arm and operable asan incident to the positioning of the latter to deenergize said solenoidand thereby render effective said second compression spring.

10. In a hydraulic control system of the type described, an actuator, acontrol valve for deflning an operating cycle for said actuator inresponse to being moved through a series of successive steps, a movableabutment having a lostmotion connection with said valve and shiftableinto a plurality of axial positions with respect to said valve,electromagnetic means for rendering said movable abutment effective todirectly position said valve in certain of said successive steps, andmeans responsive tc the positioning of said movable abutment forrendering said abutment 1s i effective to indirectly position said valvein the remaining of said successive steps.

1l. In a'hydraulic control system of the type described, an actuator, acontrol valve having a cylindrical bore, an axially shiftable plungerslidably disposed within said bore for dening an operating cycle forsaid actuator in response to being moved through a series of successivesteps including the steps of rapid traverse forward, first feed forward,second feed forward, rapid traverse return, and stop, a rocker armhaving a lost-motion connection with said plunger and shiftable into aplurality of axial positions with respect thereto, a solenoid adaptedwhen energized to yieldably urge said plunger into'abutment with saidrocker arm rendering the latter effective to directly position saidplunger in the steps of rapid traverse forward, first feed forward, andsecond feed forward, spring means associated with said plunger andadapted when said solenoid 'is deenergized to render said rocker armeffective to directly position said plunger in the stop step, and switchmeans responsive to the positioning of said rocker arm for renderingsaid rocker arm effective to indirectly position said plunger in therapid traverse return step.

12. In a hydraulic power system of the class set forth, the combinationcomprising an actuator, a control valve for defining an operating cyclefor said actuator and having a plunger axially shiftable into aplurality of positions including a rapid traverse return position,spring means associated with said plunger and adapted to bias saidplunger toward said rapid traverse return position, electromagneticmeans associated with said plunger and adaptedwhen energized to overcomethe bias of said spring means, and a pressure-actuated switch in serieswith said electromagnetic means, said switch being adapted when thepressure in said system' exceeds a predetermined value to interrupt thecircuit of said electromagnetic means thereby permitting the bias ofsaid spring means to move said valve plunger into said rapid traversereturn position.

13. In a hydraulic power system of the class set forth, the combinationcomprising an actuator, a control valve for deflning an operating cyclefor said actuator and having a plunger axially shiftable into aplurality of positions including a rapid traverse return position, acompression spring associated with said plunger and adapted to bias thelatter toward said rapid traverse return position, a solenoid associatedwith said plunger and adapted when energized to overcome the bias ofsaid compression spring, a control circuit for said solenoid and apressureactuated switch in series with said control circuit and adaptedwhen the pressure in said system exceeds a predetermined value tointerrupt said control circuit, thereby deenergizing said solenoid andpermitting the bias of said spring means to move said plunger into saidrapid traverse return position.

14. In a hydraulic power unit of the class described, the combinationcomprising a main control valve having an axially shiftable valveplunger, electromagnetic means for yieldably applying a force to saidplunger, spring means for yieldably applying a force to said plunger inopposition to the force of said electromagnetic means, a reciprocatorytripping bar, a rockable abutment member movable intermittently by saidreciprocatory tripping bar and disposed between said bar and said valveplunger, the position of said abutment member serving to govern thesequential application to said valve plunger of various combinations offorces directly by said electromagnetic and said spring means andindirectly by said tripping bar.

15. In a hydraulic power unit of the class described, the combinationcomprising a main control valve having an axially shiftable valve spool,solenoid means for yieldably applying a force to said valve spool,spring means for yieldably applying a force to said spool in oppositionto the force of said solenoid means, a slidable dog bar, a rocker armmovable only by said dog bar for intermittently applying a positiveforce to said spool to position the latter, said rocker arm having africtional mounting adapted to exert a neutralizing force on said valvespool in opposition to the resultant of the forces of said solenoid andsaid spring means, the position of said rocker arm serving to govern thesequential application to said valve spool of various combinations offorces directly by said solenoid means and said spring means andindirectly by said tripping bar.

16. In a hydraulic pou-'er system having a main control valve of thecharacter set forth, the combination comprising a housing having aported cylindrical bore, a valve plunffer slidably disposed within thebore and shiftable into a plurality of control positions, a movableabutment having a lost-motion connection with said valve plunger forshifting the same into said control positions, and releasable means formoving said plunger to take up the slack in said lost-motion connection,said means when actuated to take up such slack being adapted to strikesaid plunger a hammer blow to free the latter if stuck.

17. In a hydraulic power system having a main control valve of thecharacter set forth, the combination comprising a housing having aported cylindrical bore, a valve plunger slidably disposed within thebore and shiftable into a plurality of control positions, a movableabutment having a lost-motion connection with said valve plunger forshifting the same into said control positions, releasable meansincluding a solenoid for imparting motion to said plunger through alimited distance and in either of two directions in order to take up theslack in said lost-motion connection, and abutment means carried by saidreleasable means for striking said plunger a hammer blow to free thelatter if stuck.

18. In a hydraulic power system having a main control valve including avalve plunger slidably housed within a ported cylindrical bore andshiftable axially into a plurality of control positions, the combinationcomprising a tension rod slidably disposed within an axial bore in saidvalve plunger, an abutment rigidly attached to said tension rod adjacentone end thereof, a compression spring mounted on said tension rodbetween said abutment and one end of the bore in said plunger, anannular abutment within said plunger adjacent the opposite end of thebore thereof and engageable by said abutment on said tension rod, a headportion unitary with said tension rod and defining coplanar shouldersthereon, an external annular face at the extremity of said valve plungeraway from said annular abutment and adapted for engagement with saidcoplanar shoulders on said tension rod, and a solenoid including amovable core coupled to said tension arm and adapted upon beingenergized to fully compress said compression spring thereby bringingsaid abutment on said tens'on arm sharply into engagement with saidannular abutment of said valve plunger so as t free the latter formovement in one direction 'if stuck, said compression spring beingadapted upon the deenergizing of said solenoid to produce an impactbetween said coplanar' shoulders and said external annular face of saidvalve plunger s0 as to free the latter for movement in the oppositedirection if stuck.

19. A hydraulic control system for machine tools and the likecomprising, in combination, an

actuator, a pump, a sump, iiuid conduits leading from the actuator, thepump and the sump respectively, a main control valve connected with saidfluid conduits for delivering fluid to and receiving fluid from saidactuator, a valve spool slidably disposed within a ported bore in saidmain control valve for directingv the movements of said actuator inresponse to movement of said valve spool through a series ofpredetermined axial positions, a rocker arm having a lost-motionconnection with said valve spool, said rocker arm being movable into alesser number of positions than said valve spool, a tripping bar movablewith said actuator and adapted to position said rocker arm, a rst meansfor taking up the slack of said lost-motion connection in one directionto permit the definition by said rocker arm of certain ones of saidaxial positions of said Valve spool, said iirst means being renderedeffective or ineffective in response to the position of said rocker arm,and a second means adapted, upon the rendering ineffective of said rstmeans, to take up the slack of said lost-motion connection in theopposite direction and thus permit the definition by said rocker arm ofthe remainder of said axial positions of said valve spool.

20. A hydraulic control system for machine tools and the likecomprising, in combination, an actuator, a pump, a. sump, pressure andexhaust conduits leading from the pump and the' sump respectively,conduits leading from said actuator, a main control valve connected withsaid pressure and exhaust conduits and said conduits leading from saidactuator for delivering fluid to and receiving fluid from said actuator,a valve spool slidably disposed within a ported bore in said maincontrol valve for effecting a sequence of movements of said actuator inresponse to movement of said spool through a predetermined sequence ofaxial positions, a rocker arm having a lost-motion connection with saidvalve spool, said rocker arm being movable into a lesser number ofpositions than said valve spool, a tripping bar rigidly attached to saidactuator and adapted to position said rocker arm, releasable means fortaking up the slack of said lost-motion connection in one direction topermit the dennition by said rocker arm of certain ones of said axialpositions of said valve spool, said releasable means being susceptibleof actuation by said rocker arm, and resilient means for taking up theslack of said lost-motion connection in the opposite direction to permitthe denition by said rocker arm of the remainder of said axial positionsof said valve spool.

2l. A hydraulic control system for machine tools and the likecomprising, in combination, an actuator, a variable delivery pump, asump, pressure and exhaust conduits leading from the pump and the sumprespectively, conduits leading from said actuator, a main control valveconnected with said pressure and exhaust conduits and said conduitsleading from said actuator for delivering fluid to and receiving fluidfrom said actuator, a reciprocable valve spool disposed within a portedbore in said main control valve, said valve spool being shiftable into aplurality of positions for defining a stepped sequence of actuatormovements including the steps of rapid traverse forward, rst feedforward, second feed forward, rapid traverse return, and stop, a rockerarm adapted to define said valve spool positions but s movable itselfinto a lesser number of positions, a.

tripping bar rigidly attached to said vactuator for moving said rockerarm, a lost-motion connection between said rocker arm and said valvespool. electromagnetic means adapted to exert a force in one directiontending to take up the slack of said lost-motion connection, and springmeans effective upon deenergizing of said electromag- 22 netic means toexert a force tending to take up said slack in the opposite direction.

MAX A. MATHYS.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PTnNTs lo Number Name Date 1,787,781 Galloway Jan. 6, 19312,161,156 Goehring June 6, 1939 2,259,636 Harrington Oct. 21, 19412,274,603 Herman et al. Feb. 24, 1942

